1. Field of the Invention
The present invention relates to a via structure that reduce inductance in the current path when used in printed circuit boards and integrated circuits.
2. Description of the Related Art
A printed circuit board comprises a thin plate formed of multiple layers onto which chips and other electronic components, such as integrated circuits, are mounted. Computers consist of one or more boards, often called cards or adapters. Each layer of the printed circuit board includes metal paths ending in contact pads. An electronic device would transfer signals to a network of metal paths through the contact pad to communicate over the metal paths with other electronic devices on the same or different layers of the substrate. A via structure extends through holes in the layers and interfaces with contact pads on different layers to allow signals to travel between layers through the via. In this way, the via provides a conductive path to communicate between conductive layers.
A forward current or signal transmitted from a source device on one layer to a target device on another will pass through a via. After reaching the target device, a return current will travel on one or more voltage layers, such as a ground layer, to the source device that initiated the current. The return current will attempt to follow the path closest to the original signal on the voltage layer to take the path of least impedence. However, the return current may have to diverge from the closest path of the forward current to a structure, such as another via or a decoupling cap, in order to move from one voltage layer to another that is in communication with the source device. This divergence from the closest path following the signal trace path of the forward current increases the loop area of the forward and return currents. Increasing the loop area results in a corresponding increase in inductance and, hence, electronic emissions, i.e., noise. Such increased emissions and noise increases cross-talk, interferes with other signals in the system and can radiate from the card.
Thus, there is a need in the art for improved techniques for controlling the path of the return current in order to minimize inductance and electronic emissions and interference.
To overcome the limitations in the prior art described above, preferred embodiments disclose a via for use in a printed circuit board or integrated circuit having first, second, third, and fourth layers. The via includes a first path capable of transmitting a forward current from the first to the second layer and a second path capable of transmitting a return current resulting from the forward current from the third to the fourth layer to return to a source of the forward current.
By providing paths in the same via structure for the forward and return current, preferred embodiments allow the return current to follow the closest path on a different plane to the signal trace of the forward current, thereby minimizing the loop area and reducing inductance.